We only have one pest genus: Oscillitoria. They really are not heterocyst forming BGA's, but they might still fix N2 gas nonetheless. Phormidium I found in a few samples also, semi rare though and the tank was nasty.

i have also found lyngbya. i think its commonly misdiagnosed.
generally it wont form a thick mat in a tank, but i have seen it growing entangled in plants before. it can make for quite a mess...

I do not think any said they cannot use NO3, we have stated that BGA is correlated with a reduced NO3 level(under 5ppm), to the point where it starts affecting plant growth(eg, limited N for plants). Limiting PO4 does not cause any algae bloom really(GSA mostly), so that was popular in the 1990's and not NO3 limiting.

i didnt mean to imply anyone here in this thread claimed that that BGA cant use NO3, but i have heard others make the argument that lack of NO3 is THE cause for BGA...
i wouldnt expect limiting PO4 to cause an algae bloom... in fact, its still a common practice to regulate algae and cyano in many lakes.

This(lower NO3 below 5ppm(?) appears to induce Oscillitoria in planted tanks. There is no way to limit nutrients for BGA's in planted tanks, their demand for nutrients are minute compared to plants.

oscillitoria practically forms its own ecosystem. the mucilage it produces harbors a LOT of life, which can recycle just about anything... so yes, i dont think it can be killed out right by promoting plant growth, but i do believe you can slow it from spreading or stop it from spreading. if its missing something, it just slowly dies or disseminates and dissimulates its presence(ie, under the gravel, along the tank glass).

Indirectly, plant growth appears to suppress algae.
Perhaps when BGA's detect lower O2 in the root zone, or the vegetative cone, they will bloom and grow. Plants are not growing, it's a good time to grow. Otherwise, they just sit there. Mostly between the glass and gravel below the soil a little bit.

Once the NO3 drops, then they bloom.

i set up a lot of tanks taylored to growing algae. i have come to learn that there isnt any one thing that causes a BGA bloom. i have had bare bottom tanks with high nitrates(over 80ppm) that grew more cyano than i knew what to do with, and some with no nitrates and plants present that just refused to grow cyano.

I do not think ANYONE has ever suggested that we are limiting BGA with nutrients.

i would have to disagree...

So you think that BGA are now micronutrient limited, whereas you argued above that they cannot be N limited? Leaching from plants provides ample supply, a few decayed leaves is all that is needed.

So what ppb of micro nutrients are limiting to Oscillitoria?
Any ideas? Estimations?

no clue! more than i currently have on one tank and less than in another

BGA does not get energy from N fixation, it's a energy expenditure(i think you meant to say this).yes, i meant to say growth, which of course, requirse energy to be spent on nitrogen.
Not that Oscillitoria even needs to fix N2 gas in any planted tank, there's always non limiting N in a planted tank for most any algae or BGA.

If not, we should easily be able to water change algae into submission for a few days before the plant reserves are depleted. Generally that leads to worse problems(again, back to poor plant growth as the root cause, not nutrient limitation of algae/BGA).

I know of no submersed plant that has the same rate of growth at high KH as they do at high CO2. CO2 is greatly preferred in each and every case. It's an added allocation and energy expense to use HCO3 vs CO2.

I know of many aggressive weeds that use HCO3 as a carbon source indirectly, but it's still an energy expense in all cases.

i wouldnt call it an energy expense... less efficient and less preferred, ill give you that.

I add lots of PO4, roughly 15 ppm a week from KH2PO4, my KH is low, about 20 ppm. BGA issues? I do not have any. I tend to care for my tanks well, however clients often are not consistent.

BGA is present in all my tanks, but it's regulated to the gravel below the surface on the glass nearest to a light source. It'll stay there for years, so it's not a question of having it inoculated or present, rather, is it a management issue?

No, not in the least.

We can rule out things like PO4, low KH, etc as direct factors.
I think you might be on to something with O2 however.

When plants are limited, mild moderate or strongly, then they reduce growth and also reduce O2 evolution from leaves(veg cones/apical meristems etc) and also roots. They do not release much O2 at night. Indirect growth reduction might be a trigger for many species of algae.

Bacterial links to the O2 levels might be a player also. No one really knows.

that brings up something i forgot to mention; stratification doesnt occur in a tank with decent flow, but since the most common cyano we deal with in tanks forms fibrous mats covered in mucilage, the oxygen can quickly deplete underneath it. in testing cyano as a feed for microfauna, i used to turn all sources of flow off and then turn the lights off for a day. i would then turn it back on and a lot of the cyano would have lifted from its substrate(presumably because the underlying mucilage sheath deteriorated). from there i would blend it up and keep it in suspension. it only seemed to work well for feeding sessile philodina.

Well, that is a NEW one, lasers. it isnt new actually, its one of the techniques i learned when i worked for the university of florida. the idea is to flood cyano with light, causing it to produce a lot of oxygen, something it does well. a petri dish would have cyano added to it and whatever was going to be observed would be placed in the center of the dish. a 265-nm diode was focused into the area where the specimen was to be observed. a small shield was used to shadow the subject from the uv, with the end result being a critter that was heavily drugged being able to be observed, alive and unmoving, for extended periods of time.

the cyano wont grow in the presence of UVC, so it kept a barrier up that prevented the filaments from moving into the field of view. i use also use UVC for mutagenesis from time to time, and have seen how fast it can kill anything really really small.
for cyano though, it would be a bandaid...

of all the fascinating aspects of an aquarium, none bring me such felicity as the deceptively complex simplicities of our microfauna.

well, if no one thing works, i would suggest a combination of the easiest things first. ie, increase nitrates and raise CO2 and reduce photoperiod. when its gone, you can start slowly lowering CO2, increasing photoperiod, back off on nitrates, etc, until you find out what the threshold is for your tank.

the only thing i dont like about antibiotics is that it doesnt engender a change that is capable of preventing the problem from coming back. it may never come back, but if it does you will be back to square one...

i think we jump the gun a bit when we tell people a quick fix way of treating it without explaining why it might work.

It's been about a week now and it's worked great! I do have small spots of BGA still but 90% of it has died! Since doing all this work my nitrates have come up from 5PPM to 10-15PPM, not sure if that helped at all.

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